How Fast can I go?

[Tim Butler]

I asked you guys about a prop for my boat a 1993 classic 18
I have a cleaver 27 pitch on it running 63mph at 4200 rpms can I get more? 351ci.


Thanks Tim

[Sam]

Not knowing all the facts and specs it sounds a little on the slugish side. Have you checked to see where your prop slip numbers are.

Sam

[GKricheldorf]

Here is a link that will help you calculate your top speed.

http://www.csgnetwork.com/marinepropcalc.html

[MOP]

I think your RPM is too low, I would have it 48-5000. I would borrow a 21 and see what happens. :fire: :fire:

******* Fixed **********
Sorry!
Was on phone headed for the door, screwed this up one royally! 200RPM per inch 25 maybe 26 no cup. Then again what about 24" 4?

Phil

[Ranman]

MOP, Based on what Tim is saying, isn't that a bit drastic of a drop? I would start with a 25P or even better, a 23P and see where the RPM's go from there.

[Barry Phillips]

I was running a 23" Vengeance on my 350/250 HP 18 spinning between 46 and 4,8000 rpm, depending on load, weather etc. The boat ran 63 to 65 mph with this setup. I tried a 21" Mirage Plus, gained 200 rpm and lost 3 mph. Donzi sets up new 18s from the factory with 23" wheels and in my situation this size worked best. I think a 27" is way to much prop for a small block to turn on less it's makeing a lot of power. 4,200 rpm is way to low. Donzi has shipped big block 22s with 23" and 25" props. My 496 mag equipped 22 runs a 23" Mirage Plus and it makes 70 mph at 5,000 rpm non confirmed.

[boldts]

Tim,

4200 rpm's seems low for a small block Ford engine. While I don't know what the recommended r's for your engine are, I think there is room for more.

General rule is 2 to 300 rpm's for every 1" of pitch subtracted. So with that being said, I think your engine would be happier turning a 25" prop. What concerns me though is that Clevers are known for more slippage and your still only turning 4200.

Since you have a baseline, the next thing to do is play with a prop calculator and try different prop pitchs using the 200 rpms per 1" rule. In other words, put a 26" pitch in at 4400 rpms with your outdrive gear ratio and see if the speed increases.

Let me use my Classic as a guide. My boat came with a 23" pitch prop and 1.36:1 gear ratio turning 4500 at WOT trimmed out. Now using this, and my engine's prefered engine RPM's being 5000, you would think my boat using the rule needs a 21" pitch. How-ever, what I found was that even though the engine was turning 5000 rpm's, the speed did not increase over a 22" pitch turning 4800 to 4900 trimmed out. So, I went with a 22" pitch and am running fewer rpm's to save the stress on the engine.

Best thing you can do, is go to a marina where they allow you to try different size props. Put a prop on in a smaller pitch, take your GPS and see how the boat performs. You never know, you may already have the best performing prop on your boat, but I'd venture to guess with some tweaking, you'll be able to make it better. Another idea and one that I would prefer, is join up with the GA gang coming to the Awakening of the Horses gathering on Lake Cumberland May 20th thru 23rd. Turbo propellers will be at the gathering along with represenitives to answer questions. They also bring a supply of props for everyone interested to try. They will help you set up your boat and if they don't have the prop you need, at least you'll know what to order when you get back home. Oh, BTW, it's a great time with some fantastic people attending on a lake that is fresh and lots of room to let the horses run!

[bigman]

Tim , I've got a 68,18' classic with a 350, Mag. 300 H.P. I have a 23 Mirage Plus. If I trim it out and can deal with the chinewalk I can over spin the engine. I don't have G.P.S. I believe it could handle a 25, not a 27. I think it would over spine a 21 pretty easy though. All boats are diffrent and most of thes guys know more about them than I do, but maybe this might help, bigman.

[Last Tango]

I have a 2001 Classic 18 with a 377ci/320hp Merc, Bravo 1 with 1.5 ratio and a Mirage 23P. Spins the motor to 5000rpm. Motor is rated to 5250. I played witha 24p (too much) and a 22p (too little). Huge difference in the boat with these three props. Boat originally came from the factory with a 25p but would only spin it to 4500rpm when new. Motor and drive now have 125 hours. Everything seems to be working just fine with this combo although I have tried other props.

[KRAVEN]

I have a 2002 18 with 377ci/377hp spinning 25 mirage 2 lab finished.Ispin 5000rpm and have run 75+ on gps. :)

[MOP]

Patched my first post! Still extracting cranium! :bonk:

MOP

[MLerner]

Hi Tim,

I have a 1993 18 with a 351 (5.8) Cobra outdrive. Sounds like yours. Would be interesting to compare notes. I'm spinning a 21 x 14.75 Viper prop (stock is a 21 x14.25 Viper, which I still have) at around 4200-4400 (recommended for this moter). Curious to know how your rpms are the same with a 27 Cleaver. GPS on the old prop is about 59 mph. New prop is supposed to provide more mph. Will let yu now when I test it in a few weeks.

Best, Michael

[zanimals]

What kind of engine? 5 liter or 5.8L? I have a 5.8L and a Viper 3 blade stainless and I do 71 (on flat calm).


I asked you guys about a prop for my boat a 1993 classic 18
I have a cleaver 27 pitch on it running 63mph at 4200 rpms can I get more? 351ci.


Thanks Tim

[cutwater]

What kind of engine? 5 liter or 5.8L? I have a 5.8L and a Viper 3 blade stainless and I do 71 (on flat calm).

Tim hasn't logged in since Jan '05.